The use of the bow and arrow dates back to ancient civilizations. In such times, primitive bows were made from elastic wooden limbs, and arrows were made from wooden shafts with points made from flint on the leading edge of the arrow, and feathers attached to the trailing edge. For many centuries, the bow and arrow was an essential weapon during wartime, and a necessary tool for hunting. However, with the development of firearms, archery had become nearly obsolete.
In the 1920s, professional engineers took an interest in archery and led the commercial development of new forms of the traditional bow, including the modern recurve and compound bow. These modern bow forms are now dominant in modern Western archery. Of the two, the compound bow has become the most widely used type of bow for all forms of hunting in North America.
One form of compound bow commonly in use today is the crossbow. A crossbow consists of a typical bow, either recurve or compound, that is attached to a stock which holds the drawn string. Crossbows have a much smaller draw length than standard bows. As a result, for the same energy to be imparted to the arrow (or bolt) the crossbow has to have a much higher draw weight. Indeed, the draw weight of modern crossbows is several times greater than traditional bows. The draw used to load the crossbow is stored in the bow as elastic potential energy, and when the bowstring is released, this stored energy is imparted to the arrow very quickly. The higher draw weight on the bowstring translates to a greater launching force being applied to the crossbow arrow, or bolt, and a higher initial velocity.
Modern arrows are made to a specified ‘spine’, or stiffness rating. Typically, in order to maintain accuracy during use, a bolt was necessarily very rigid and capable of withstanding the excessive forces from a crossbow. This mandated a bolt having a large shaft cross section that provided the strength that was required. As a result of this large shaft cross-section, a bolt is typically significantly heavier than a standard arrow.
Nearly all crossbows are manufactured to receive a commonly sized bolt. Specifically, bolts are typically 20″ to 22″, have an outside diameter of 0.344 inches, and have a mass of roughly 15 grains per inch, including vanes, nock, and inserts. There has traditionally been very little variation in the bolts available on the market. While they may vary slightly in length, the overall shaft diameter and weight-per-inch of the shaft remain relatively constant. As a result, there are very few options for the crossbow hunter when considering bolts.
One challenge facing crossbow hunters is the instability that develops shortly after shooting a crossbow bolt. Specifically, in use, a fletching vane of the crossbow bolt is inserted into a channel formed in the crossbow rail. This channel runs the length of the crossbow, and maintains the position of the bolt on the rail as it is shot from the crossbow. However, due to the positioning of the vane within the channel, and the narrowness of the channel, the vane cannot be attached to the shaft in a helical or offset position. Instead, the vane must be straight, or substantially in alignment with the arrow shaft and channel. This results in a bolt that has insufficient rotation during flight to maintain accuracy past fifty yards.
Helical and offset vane arrangements impart a rolling moment on the bolt in flight, increasing accuracy. This principle is akin to the rifling of a bullet or spiral of a football. Where an offset vane is straight back as it is attached the vane axis is offset from the bolt shaft axis. Helical vanes have a similar offset position but are also curved in a helical manner.
Another challenge facing crossbow hunters is the standardization of crossbow bolt weights. Typically, a crossbow bolt is designed to weigh 425 grains including the vanes, nock, insert, and broad head. While this standardization is intended to facilitate use of the bolts on crossbows designed to shoot 425 grain bolts, it nevertheless minimizes the options available to crossbow hunters to optimize the flight characteristics, accuracy and effectiveness of the bolt.
In light of the above, it would be advantageous to provide a crossbow bolt that is lighter weight than traditional crossbow bolts. It would also be advantageous to provide a crossbow bolt that travels faster than traditional crossbow bolts. It would also be advantageous to provide a crossbow bolt that delivers greater kinetic energy to a target. It is further advantageous to provide a crossbow bolt that is relatively easy to manufacture and comparatively cost effective. It is also advantageous to provide a method of retrofitting traditional arrows for use in a standard crossbow.